/*
 * Copyright 2002-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.core.io.support;

import org.springframework.core.io.InputStreamSource;
import org.springframework.core.io.Resource;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;
import org.springframework.util.ObjectUtils;

import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.Reader;
import java.nio.charset.Charset;

/**
 * Holder that combines a {@link Resource} descriptor with a specific encoding
 * or {@code Charset} to be used for reading from the resource.
 *
 * <p>Used as an argument for operations that support reading content with
 * a specific encoding, typically via a {@code java.io.Reader}.
 *
 * @author Juergen Hoeller
 * @author Sam Brannen
 * @see Resource#getInputStream()
 * @see java.io.Reader
 * @see java.nio.charset.Charset
 * @since 1.2.6
 */
public class EncodedResource implements InputStreamSource {

    private final Resource resource;

    @Nullable
    private final String encoding;

    @Nullable
    private final Charset charset;


    /**
     * Create a new {@code EncodedResource} for the given {@code Resource},
     * not specifying an explicit encoding or {@code Charset}.
     *
     * @param resource the {@code Resource} to hold (never {@code null})
     */
    public EncodedResource(Resource resource) {
        this(resource, null, null);
    }

    /**
     * Create a new {@code EncodedResource} for the given {@code Resource},
     * using the specified {@code encoding}.
     *
     * @param resource the {@code Resource} to hold (never {@code null})
     * @param encoding the encoding to use for reading from the resource
     */
    public EncodedResource(Resource resource, @Nullable String encoding) {
        this(resource, encoding, null);
    }

    /**
     * Create a new {@code EncodedResource} for the given {@code Resource},
     * using the specified {@code Charset}.
     *
     * @param resource the {@code Resource} to hold (never {@code null})
     * @param charset  the {@code Charset} to use for reading from the resource
     */
    public EncodedResource(Resource resource, @Nullable Charset charset) {
        this(resource, null, charset);
    }

    /**
     *
     * @param resource 资源
     * @param encoding 编码
     * @param charset 编码
     */
    private EncodedResource(Resource resource, @Nullable String encoding, @Nullable Charset charset) {
        super();
        Assert.notNull(resource, "Resource must not be null");
        this.resource = resource;
        this.encoding = encoding;
        this.charset = charset;
    }


    /**
     * Return the {@code Resource} held by this {@code EncodedResource}.
     */
    public final Resource getResource() {
        return this.resource;
    }

    /**
     * Return the encoding to use for reading from the {@linkplain #getResource() resource},
     * or {@code null} if none specified.
     */
    @Nullable
    public final String getEncoding() {
        return this.encoding;
    }

    /**
     * Return the {@code Charset} to use for reading from the {@linkplain #getResource() resource},
     * or {@code null} if none specified.
     */
    @Nullable
    public final Charset getCharset() {
        return this.charset;
    }

    /**
     * Determine whether a {@link Reader} is required as opposed to an {@link InputStream},
     * i.e. whether an {@linkplain #getEncoding() encoding} or a {@link #getCharset() Charset}
     * has been specified.
     *
     * @see #getReader()
     * @see #getInputStream()
     */
    public boolean requiresReader() {
        return (this.encoding != null || this.charset != null);
    }

    /**
     * Open a {@code java.io.Reader} for the specified resource, using the specified
     * {@link #getCharset() Charset} or {@linkplain #getEncoding() encoding}
     * (if any).
     *
     * 获取reader返回不同编码的解析
     * @throws IOException if opening the Reader failed
     * @see #requiresReader()
     * @see #getInputStream()
     */
    public Reader getReader() throws IOException {
        if (this.charset != null) {
            return new InputStreamReader(this.resource.getInputStream(), this.charset);
        }
        else if (this.encoding != null) {
            return new InputStreamReader(this.resource.getInputStream(), this.encoding);
        }
        else {
            return new InputStreamReader(this.resource.getInputStream());
        }
    }

    /**
     * Open an {@code InputStream} for the specified resource, ignoring any specified
     * {@link #getCharset() Charset} or {@linkplain #getEncoding() encoding}.
     *
     * @throws IOException if opening the InputStream failed
     * @see #requiresReader()
     * @see #getReader()
     */
    @Override
    public InputStream getInputStream() throws IOException {
        return this.resource.getInputStream();
    }


    @Override
    public boolean equals(Object other) {
        if (this == other) {
            return true;
        }
        if (!(other instanceof EncodedResource)) {
            return false;
        }
        EncodedResource otherResource = (EncodedResource) other;
        return (this.resource.equals(otherResource.resource) &&
                ObjectUtils.nullSafeEquals(this.charset, otherResource.charset) &&
                ObjectUtils.nullSafeEquals(this.encoding, otherResource.encoding));
    }

    @Override
    public int hashCode() {
        return this.resource.hashCode();
    }

    @Override
    public String toString() {
        return this.resource.toString();
    }

}
